1. Field of the Invention
Aspects of the present invention generally relate to control systems for a power generation system having thermal energy and thermodynamic engine components.
2. Background of the Art
Environmental concerns and political and economic forces have renewed the interest in all facets of alternative energy. Many sources of alternative energy, particularly solar energy, still have tremendous potential for greater adoption. Despite the distinct advantages of emitting little or no pollution or greenhouse gasses, having an unlimited free energy supply, and being harnessed with many already proven technologies, solar energy requires further development of its technologies to make it a cost competitive energy source for heat and electricity for residences and commercial buildings compared with heat and electricity now produced by burning coal, natural gas, and oil.
Solar electric generating systems suitable for distributed electric power generation or installation on residential or commercial buildings typically use photovoltaic semiconductor technologies that convert sunlight directly into electricity. Although viable in some applications, existing photovoltaic solutions are too inefficient and cost prohibitive to be broadly adopted as an electric energy source or thermal energy source. Similarly scaled solar thermal systems are used for space and domestic hot water heating, but have no provision for electric power generation, and cannot reconcile the disparity between the high demands for thermal energy in cold months with the high availability of thermal energy in warm months. Because they are limited to producing only one form of energy, either electricity or heat but not both, neither solar energy platform can by itself practically address both electrical and thermal energy needs of residential or commercial buildings.
Recent advances in heat engine technology have rendered it feasible to incorporate a heat engine, such as a Stirling engine, into a solar thermal energy system and thereby use solar thermal energy to generate electricity in a distributed or in a combined distributed and grid-tied configuration. Heat energy delivered directly from a solar thermal energy collector or from solar thermal energy previously stored in a storage location is supplied to the heat engine, which in turn drives a generator to produce electricity. The heat engine may be used solely to generate the electricity for a structure, such as a residence, office or small industrial facility (collectively referred to as “building”) at a given moment of time. However, as the electrical demand in the building will fluctuate over time, including during a day, during a week and over a yearly seasonal cycle, the heat engine may be unable to provide the entire electrical load at some times, or may be able to supply excess electricity at other times. For example, during cloudy conditions and storms, the solar irradiation on the collector is disrupted, requiring the use of a non-solar energy source, which may include grid-supplied electricity, to meet the electric power requirements of the building. Furthermore, it may also be desirable to use the solar thermal energy provided from a solar collector for space and water heating applications, thus creating a conflict between the need for electricity and the need for space and domestic hot water heating.
Where solar thermal energy is used solely for thermal heating, such as space and domestic hot water heating, the choice of how to use the thermal energy is rather straightforward: One or the other use is prioritized, and if inadequate thermal energy is available to meet both needs, then an additional energy source, such as natural gas provided by a utility, is used to provide the energy difference. However, where the solar thermal energy may be used to generate electricity (solely or in combination with heating demands), the optimal use of the energy is a function of a number of additional factors, including the immediate and future cost of electricity or other energy source, the time of day, the expected heating needs as compared to the electrical needs of the building and residents, the season of the year and any expected weather changes, such as approaching cold fronts, warm fronts or storms.
Thus, there is a need in the art for distributed energy distribution systems and combined distributed and grid-tied energy systems which enable the user to better optimize, or alternatively, enable intelligent selection of the use of the thermal energy supplied by a solar thermal collector or other local thermal energy source, and thereby increase the rate of return available from the investment in such a system.